IP Multimedia Subsystem IMS is the technology defined by the Third Generation Partnership Project 3GPP to provide IP Multimedia services over mobile communication networks (3GPP TS 22.228, TS 23.228, TS 24.229, TS 29.228, TS 29.229, TS 29.328 and TS 29.329 Release 5 and Release 6). IMS provides key features to enrich the end-user person-to-person communication experience through the use of standardized IMS Service Enablers, which facilitate new rich person-to-person (client-to-client) communication services as well as person-to-content (client-to-server) services over IP-based networks. The IMS makes use of the Session Initiation Protocol SIP to set up and control calls or sessions between user terminals (or user terminals and application servers). The Session Description Protocol SDP, carried by SIP signaling, is used to describe and negotiate the media components of the session. Whilst SIP was created as a user-to-user protocol, IMS allows operators and service providers to control user access to services and to charge users accordingly.
IP Multimedia services provide a dynamic combination of voice, video, messaging, data, etc. within the same session. By growing the number of basic applications and the media which it is possible to combine, the number of services offered to the end users will grow, and the inter-personal communication experience will be enriched. This will lead to a new generation of personalized, rich multimedia communication services, including so-called “combinational IP Multimedia” services.
The concept behind combinational services involves bundling the voice service in an existing circuit-switched CS domain with the “content” in the packet-switched PS domain. It uses standards-based voice and data networks that are, to a great extent, already in use by operators. An example of combinational services is when a voice call is setup as normal in the CS domain and then while the call is ongoing, content such as images, videos and files can be added or dropped via the PS domain. It enriches voice communication and improves the interaction between voice and data services creating a number of new business opportunities for mobile operators. The combinational services end-to-end solution is highly scalable, robust and aligned with the 3GPP Combining CS and IMS services CSI specifications and is based on IMS architecture as specified by 3GPP.
Fixed IMS deployments support a variety of services like IMS Multimedia Telephony MMtel, File Transfer and Instant Messaging etc. IMS Multimedia Telephony offers new, attractive services for the residential market. Operators can expand their current Public Switched Telephone Network PSTN offering with one or several IP-telephony lines to each household. IMS Multimedia Telephony is based on IMS standard, specified by 3GPP. Furthermore the solution is built according to a standardization conducted by TISPAN that handles additional requirements from fixed network perspective. IMS Multimedia Telephony reduces costs by allowing seamless adding of new applications and evolution of services from IP Telephony to Video telephony to fixed/mobile convergence. In IMS Multimedia Telephony, a single session model is used for multiple media transportation, e.g. voice and video is negotiated and setup as one signaling session. FIG. 1 is part of the prior art and schematically discloses communication between Multimedia Telephony terminals A1 and A2 both using media transfer according to a one-session model “ONE”. The further node entities shown in FIG. 1 will be explained later in the description when the invention is discussed.
Currently CSI (Combining CS and IMS services) is a 3GPP defined service used to enrich the experience of a normal mobile circuit switched CS communication session such as voice with a simultaneous IMS session. This IMS session could be a video stream, picture transfer or other types of media transfer.
While in IMS Multimedia Telephony MMtel, voice and video is negotiated and setup as one signaling session, in the case of CSI, voice is setup with a CS session and e.g. video is setup with an IMS session in parallel i.e. MMtel uses a one session model and CSI uses a two session model. Communication between terminals using different session models poses an interworking problem.
In the US Patent Application US 2006/0126590 is disclosed a method for receiving data in a system where data is transmitted on a plurality of frequencies. A device determines a configuration associated with a selected session and receives the session in accordance with a determined configuration. In a CSI to MMtel scenario the mismatch concerns a one-way session in relation to a two-way session where the second session could result in a busy response from the MMtel client.
A further problem is the necessity to do session re-routing. The US Patent Application US 2004/0160895 A1 discloses a failure notification followed by an appropriate re-routing.
A voice session initiation from MMtel to CSI will result in routing into the Packet Switched domain followed by a rejection from CSI, since CSI does not support Voice over Packet Switch, only Voice over Circuit Switch. MMtel uses the IMS domain for setup according to the one-session model while CSI uses both IMS and CS domains for setup according to the two-session model. Caller Preferences for the Session Initiation Protocol can be found in standard documents such as RFC 3841.